The role of American public debt is investigated in the article as a place for riskless investments and built-in stabilizer of national economy and financial system. Reasons of wrong approaches to the public debt problem are considered. These are traditional alarms about the danger of public debt as a source of inflation. Trump’s calm attitude to the problem of growing public debt is being estimated by economists and other authors at least as a strange position of President in this situation. Nevertheless Trump hopes that the growth of the economy will somehow permit to decide the problem of the public debt. So Trump estimates the economic growth as a more important problem, than the public debt, among challenges facing U.S.A. To understand properly the problem of U.S. public debt one have to consider it as a riskless asset necessary for domestic and foreign investors. A big role of institutional investors (pension funds, mutual funds, life insurance companies e.c.) provides a big demand for treasury debt papers as riskless assets. Add here foreign central banks which need such assets for their reserves. Than one can understand that this demand provides the existence of U.S. public debt without crisis events. In this situation the public debt works as a builtin stabilizer. Taking all these aspects of the public debt, Trump and his Administration have to elaborate a conception for managing the problem properly according with modern criterions.